The present invention relates to a thin-film magnetic head with superior CSS (contact, start and stop) characteristics, particularly for use in a small-sized high-density recording magnetic disk device.
Recording-reproducing floating type magnetic heads in magnetic devices are classified into three types, namely, a monolithic type in which the whole structure thereof is formed of soft-magnetic ferrite, a composite type in which, only for an electromagnetic transducer portion, a soft-magnetic Mn--Zn ferrite core or a magnetic head core with a metal magnetic thin film is produced and incorporated in a slider formed of a nonmagnetic material, and a thin-film type in which an electromagnetic transducer portion formed of a metal magnetic thin film is provided on a nonmagnetic substrate.
Composite type magnetic heads are mainly used as floating type magnetic heads for 3.5-inch or less than 3.5-inch high-density small magnetic disk devices. With the advance of increase of the recording density, there is a tendency to use more frequently thin-film type magnetic heads in which an electromagnetic transducer portion is formed on a nonmagnetic substrate by lithographic and thin-film techniques, and which have been heretofore mainly employed in large-sized devices.
The nonmagnetic slider used in thin-film type heads requires optimum relations in coefficient of thermal expansion from the double point of view of production and use because a metal magnetic film is formed on an Al.sub.2 O.sub.3 film generally formed on a trailing edge of the slider. From such relations, a substrate material formed of alumina titanium carbide (ATC) as a main material is generally used for the slider.
In order to meet the recent advance of increase of the recording density in magnetic disk devices, hard disks of the type in which a magnetic substance is closely deposited onto a disk substrate through plating or sputtering, are used as magnetic recording media.
The surface of the disk produced through plating or sputtering as described above is finished up with flat and fine surface roughness compared with the conventional coating type disk and is overcoated with a lubricant. Accordingly, the sticking phenomenon which occurs in between the head and the disk surface has come up to a serious problem though it was a minor problem up to now. That is, as the surface roughness of the surface facing the magnetic recording medium becomes finer, there arises a phenomenon that the surface of the disk in a state of rest is stuck to the surface of the head facing the disk. When the adhesion between the head and the disk becomes intensive excessively, the adhesion exceeds motor torque for rotating the disk so that the device cannot operate easily. At the same time, the lifetime against CSS (contact, start, and stop) operations is shortened. In particular, in the case where a plurality of disks are used in combination, the problem becomes more serious.
In order to relieve the sticking phenomenon, various means for treating the surface of the head facing the disk to make it rough to some degree have been proposed.
As one of the means for solving the problem, Japanese Patent Unexamined Publication No. Hei. 1-251308 (U.S. Pat. No. 5,010,429) discloses a floating type magnetic head formed of a polycrystalline material, in which air bearing surfaces as surfaces facing a magnetic recording medium are formed with convex-concave surface having height difference of 50 to 200 .ANG. on an average and repetition pitch of convex and concave of 5 to 20 .mu.m on an average, and the portions, in which the heights of convex and concave abruptly change, extend along the grain boundaries of the polycrystals. FIG. 4 is a perspective view of a monolithic type magnetic head as an example thereof.
The monolithic type magnetic head is, however, not suitable for magnetic disk devices requiring higher-density recording in the future because the whole structure is formed of a soft-magnetic material so that this type magnetic head has disadvantages, for example, in that the inductance (L) of the head is large, therefore, it makes the high-frequency response poor and thereby produce noise easily.
FIG. 5 is a perspective view showing an example of the thin-film type magnetic head. The reference numeral 10' designates a magnetic head, 11' air bearings, 12' an electromagnetic transducer portion and 13' a slider. Alumina titanium carbide used in a substrate constituting the slider of the thin-film head, is a material in which a problem may be caused by a lubricant of the disk as a recording medium because titanium carbide is active and in which another problem may be caused in workability because it has high hardness with the Vickers hardness of about 2,000 Kg/mm.sup.2. Furthermore, it is difficult to form suitable concave-convex level differences in the surface of the head facing the magnetic recording medium. Accordingly, in particular, the CSS characteristic becomes a problem in the floating type magnetic head requiring the flying height of less than or equal to 0.1 .mu.m with the advance of reduction in size and increase in recording density.
The inventors of the present invention have disclosed nonmagnetic Mn--Zn ferrite for a magnetic head in Japanese Patent Unexamined Publication No. Hei-3-126662 and have further disclosed a composite type floating type magnetic head having a slider formed of nonmagnetic Mn--Zn ferrite in Japanese Patent Unexamined Publication No. Hei-3-127315.
The inventors of the present invention have made further researches and, as a result, have made it possible to provide a thin-film magnetic head in which suitable concave-convex surface having height difference is given onto air bearing surfaces by using nonmagnetic Mn--Zn polycrystalline ferrite to approximate the co-efficient of thermal expansion thereof to the coefficient of thermal expansion of the Al.sub.2 O.sub.3 film formed between the slider and the metal magnetic film to thereby attain good CSS characteristic and avoid separation of the metal magnetic film.